Bouncing off the Walls

by Fiona Bayrock

How's the music in your room? Too much treble or bass? Not enough? Got extra sound bouncing around? Do certain notes always jump out at you? Check the acoustics—the sound qualities of your room.

Whether your music sounds great, barely passable, or downright awful depends on how sound waves behave when they hit different surfaces. As a rule, sound waves are reflected by hard surfaces and absorbed by soft ones, but most materials absorb and reflect high-frequency (treble) and low-frequency (bass) sounds differently.

To improve the acoustics of your room, look first to the largest surface areas—the walls, ceiling, and floor. Wood absorbs bass tones; carpet and heavy or thickly gathered draperies absorb treble; and glass, tile, concrete, and polished stone are highly reflective.

An important acoustic effect to consider in a small room, such as a bedroom, is reverberation. Large, flat, parallel surfaces, such as two walls, or the floor and ceiling, can reflect sound waves back and forth. The reflected sounds may reach your brain while the original sound is still there, but too late for the brain to register the reflected sound as part of the original. The sounds partially overlap in the brain, with the result that you hear them at the same time as a “prolonged” sound.

Reverberation is especially noticeable as extra sound in an empty room. But your furnished bedroom may also reverberate strongly to music of certain frequencies, causing specific notes to jump out each time they're played. Reduce reverberation by making the shape of your room more complex. “The wavelengths of audible sound in air can range from less than an inch to tens of feet,” says Dr. Dewey Lawson, a physicist at Duke University. “Ideally, the boundaries of listening rooms should be ‘rough’ [and] over that whole range of sizes.”

Bookshelves with books, plants, or collectibles; a wooden mask collection hung on the wall; posters mounted on foam board; pictures in deep frames; a coat rack; clothing hooks; pillows; furniture of varying heights; chunks of fabric-covered spongy foam scattered across the wall—anything that helps break up large flat wall areas—will help reduce reverberation between walls and contribute to a feeling of full and lively sound in your room.

“Typically, treating only one of a pair of opposite walls will suffice—or treating different parts of the opposite walls,” explains Lawson. Increasing the complexity of either the ceiling or the floor will also reduce reverberation between them. Aha! Clutter makes for better acoustics. At last, a scientific reason for having a messy room!

Activity

What causes reverberation? Why does reverberation interfere with hearing a sound clearly?[anno: Reverberation is caused by sound waves that are reflected back and forth in a space. Reverberation interferes with hearing a sound clearly because the brain is interpreting a sound wave as another sound wave hits the ear. The two waves overlap and cause a distortion.]

What might be another term for reverberation?[anno: Echo is another term that could be used for reverberation.]

Imagine that a woman with a high-pitched voice is singing in a room. Then she walks into another room that is the same size as the first room. The first room has bare, concrete walls and a concrete floor with a rug over it. The second room has walls with tapestries hanging on them, and a bare wood floor. How would the sound of the woman singing be different from one room to the next? Why? Write a few sentences to explain your answer.[anno: Answers may vary but could include that in the first room, the woman's voice reverberates off the walls, and the sound that reaches the listener's ears is cluttered and tinny. The rug on the floor probably does not absorb enough sound waves to keep the sound from reverberating. In the second room, the tapestries reflect fewer sound waves from the singing. Even though there is no rug on the floor, the singing probably sounds clearer in the second room.]